This invention is related to noise, sound, acoustic, and vibration reduction systems and in particular it is related to noise reduction at a source.
Electrical motors used in manufacturing, mining, food processing, and oil industries generally have a metal housing or frame that encloses all the internal motor components. Often, these motors have a fan cooling system or water cooling system to remove heat from the interior of a motor. They may also have greased bearings that are greased periodically, or bearings that are intermittently lubricated via lubrication lines. The main objective of the housing or frame is to protect the interior electrical (i.e., motor winding and armature) and mechanical (i.e., bearings, shafts) components. In general the housing is cylindrical shaped and is the main source of radiated noise to a work area. Government regulations, worker comfort and safely, and quality control are some of the reasons that the motor radiated noise much be reduced.
Current practices for reducing motor noise may be classified into three main groups: passive, active, and hybrid silencers or barriers. Current passive silencers (or barriers) are mostly used for pipes, ducts, and fan-cooled motors. They are usually comprised of two or more metallic and sound absorbing layers. In particular, passive silencers have been shown to be effective in the high frequency range (i.e., above 125 Hz). To be effective at frequencies below 500 Hz, the mass of the passive silencers can be substantial. Active silencers may be more practical in the lower frequency range. Active silencers usually have one or more sensors that are used to sample input frequency and make some adjustment via actuators or loud speakers to cancel the radiated noise. In short, the loud speakers inject a 180xc2x0 out-of-phase sound with the same frequency and magnitude in order to cancel the radiated noise. Due to limitations in data collection, data processing and actuator response times, active silencers are most practical in the lower frequency ranges (i.e., below 200 Hz).
Hybrid silencers comprise both passive and active elements. In addition to a passive multi-layer configuration, hybrid silencers usually have active features as describe above. The cost versus performance issues of the active and hybrid silencers is an on-going issue in the current market. Furthermore, current passive, active, or hybrid silencers may interfere with the heat exchanger systems of the motors. That is, if heat is not efficiently removed from the motor system, the service-free life of a motor could be significantly reduced, thereby increasing maintenance and operational cost while reducing productivity due to excess downtime.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for motor silencers that are effective in a broadband frequency range and economically viable to industries. Furthermore, a need exists for a silencer that allows for adequate cooling of the motor creating the noise.
The above mentioned problems with motor silencers and other problems are addressed by the present invention and will be understood by reading and studying the following specification. The present invention provides a motor silencer that reduces noise by providing a multi-layer shell that does not act as a secondary source of noise. A vibration bases cooling system can also be provide in embodiments of the invention.
In one embodiment, a motor silencer comprises a sound absorbing housing, and a motor mount system located inside the housing. The motor mount system uses vibration motion from a motor to pump air through the housing.
In another embodiment, a motor system comprises a motor, and a motor silencer coupled to the motor. The silencer comprises a multilayer sound absorbing housing having an inside chamber, and first and second motor mounts coupled to the motor and the housing. Each motor mount forms an air pump that pumps air through the inside chamber of the housing.
The motor mounts include an air chamber that can be compressed and expanded in response to vibrations from the motor. A one way air valve controls the direction of airflow resulting from the volume changes of the air chamber.